The present invention relates to programmed industrial robots, in general, and to means for limiting the movement of a computer controlled, anthropomorphic robot arm to within a prescribed spacial envelope to improve its operational safety, in particular.
Industrial robots are programmed mechanical devices that are capable of automatically performing material handling tasks, for extended periods of time, without human intervention. Properly applied industrial robots can increase productivity as well as relieve human operators from tasks that are excessively burdensome, boringly routine and/or dangerous. An anthropomorphic industrial robot arm has an articulated mechanical arm and hand with freedom of movement that is roughly equivalent to a human waist, shoulder, elbow and wrist. The robot's hand can be automatically positioned to any point within reach and is capable of grasping various parts or tools with relative ease. One such industrial robot is sold by Unimation, Inc. of Danbury, CT under its trademarks UNIMATE and PUMA.
Industrial robots are typically controlled by computer software or a set of instructions stored in the memory of a digital computer. The robot arm executes the material or parts positioning instructions as they are received from computer memory. These robot arm position-controlling instructions received by the robot arm are in the form of fairly precise elecrical signals whose characteristics control the type and extent of robot arm movement. Any significant variation in one or more of the characteristics associated with these robot arm position-controlling signals will produce corresponding variations in robot arm movement.
A digital computer is an electrically operated device that occasionally becomes susceptible to spurious or random electrical signals. These spurious signals may enter the computer from its power source or may be spontaneously generated within one or more of its system components. Whatever the cause of these signals, one of their effects is to cause the computer to transmit spurious positioning signals to, for example, a robot arm under its control. These spurious positioning signals may produce sudden, unpredictable robot arm movement that could cause serious injury to personnel in the vicinity of the computer-controlled robot arm.
One way to protect personnel from injury due to spurious-signal-induced robot arm movement would be to enclose the robot arm in a fairly rigid protective cage. The protective cage would preclude contact between the moving robot arm and any personnel in close proximity thereto under such circumstances. A disadvantage associated with this arrangement is that a protective cage makes it more difficult for personnel to service the robot arm during normal robot arm operation. Another way to protect personnel from such injury would be to enclose the robot arm in a system of protective light beams. If any of the beams were broken by, for example, personnel coming too close to the spacial envelope within which the robot arm is capable of operating, electrical power to the robot arm would immediately be interrupted. Disadvantages associated with this arrangement would be equipment cost and the liklihood of excessive robot arm power interruptions due to inadvertent cutting of one or more of the protective light beams controlling access to the robot arm.
A primary object of the invention, therefore, is to improve the operational safety of a computer-controlled anthropomorphic robot arm.
Another object of the present invention is to provide a simplified system for limiting the movement of a computer-controlled anthropomorphic robot arm to within a predetermined spacial envelope.
A further object of the present invention is to minimize the effects of spurious or random electrical signals on a computer that controls the positioning of an anthropomorphic robot arm.
Other objects and advantages of our invention will be made readily apparent by referring to the preferred embodiments thereof described in detail below.